Guidelines published by the National Kidney Foundation in 2002 categorize renal failure into 5 stages of increasing severity. The relation of this classification to risk stratification for operative mortality in patients with nonemergent coronary artery bypass grafting (CABG) has not been clarified. We examined the effect of chronic kidney disease (CKD) severity on CABG operative mortality in patients with nonemergent CABG. Data reporting to the California CABG outcomes reporting program is mandated in California. Data from 121 hospitals on patients undergoing CABG in 2003 and 2004 were analyzed, including clinical characteristics, CKD stage, and operative mortality. CKD stage 1 and 2 were combined to form the reference group because data on urinary markers of renal failure were not available. Excluding patients with emergent or salvage acuity for CABG, 37,735 isolated CABGs were performed. Of these, 27,132 patients (71.9%) had glomerular filtration rate (GFR)>or=60 ml/min/1.73 m2; 8,861 (23.5%) had stage 3 CKD (GFR 30 to 59); 669 (1.8%) had stage 4 CKD (GFR 15 to 29); and 1,073 (2.8%) had stage 5 CKD (GFR<15 or on dialysis). In separate multivariate analyses, GFR and CKD stage were each significantly and independently associated with operative mortality (both p<0.0001). Operative mortality increased significantly with each stage of CKD (all p<0.01). Compared with the reference group, stage 3, (odds ratio [OR] 1.18, p=0.0374), stage 4 (OR 2.23, p<0.0001), and stage 5 (OR 4.39, p<0.0001) had increasingly higher operative mortality. In conclusion, CKD stage based on National Kidney Foundation guidelines is an important predictor in risk stratification for operative mortality in patients undergoing nonemergent CABG.